Ultrasound diagnostic apparatus

ABSTRACT

An ultrasound diagnostic apparatus includes an ultrasound probe including a transducer array, and a back unit connected to the ultrasound probe by wireless communication and generating an ultrasound image based on reception signals outputted from the transducer array, the ultrasound probe including a middle unit connected to the back unit by wireless communication and a front unit detachably connected to the middle unit and including the transducer array, and the front unit having a transmission driver that supplies drive signals to the transducer array and causes the transducer array to transmit an ultrasonic beam and a preamplifier that amplifies reception signals outputted from the transducer array.

BACKGROUND OF THE INVENTION

The present invention relates to an ultrasound diagnostic apparatus andparticularly to an ultrasound diagnostic apparatus permittinginterchange of transducer arrays of an ultrasound probe.

Conventionally, ultrasound diagnostic apparatus using ultrasound imagesare employed in medicine. In general, this type of ultrasound diagnosticapparatus comprises an ultrasound probe having a built-in transducerarray and an apparatus body connected to the ultrasound probe. Theultrasound probe transmits an ultrasonic wave toward a subject, receivesan ultrasonic echo from the subject, and the apparatus body electricallyprocesses reception signals to generate an ultrasound image.

In recent years, there have been developed portable ultrasounddiagnostic apparatus that can be transported and placed near a bed orbrought to a site where emergency medical care is needed. There havealso been conceived ultrasound diagnostic apparatus having aconfiguration whereby the ultrasound probe and the apparatus body areconnected to each other by wireless communication to improveoperability. Such ultrasound diagnostic apparatus are required to beavailable in reduced dimensions for convenience.

Ultrasound diagnostic apparatus are used to diagnose subjects forvarious diagnosis purposes depending on which an appropriate frequencyband may often vary. Thus, one may consider using an ultrasound probeselected according to the diagnosis purpose from a plurality ofultrasound probes having different frequency bands kept ready for useand connecting the selected probe to the apparatus body. However,because the ultrasound probes are generally expensive, keeping aplurality of ultrasound probes available for use increases the costs.Thus, there is a demand for a transducer array that is detachablyprovided in the ultrasound probe so that a transducer array having asuitable frequency band for the diagnosis purpose may be selected andused.

For example, Patent Literature 1 describes an ultrasound diagnosticsystem wherein an ultrasound probe is comprised of a transducer headcontaining a transducer array and a beamforming module for processingthe signals from the transducer head for beamforming, and wherein thetransducer head is detachably mounted to the beamforming module.

Patent Literature 2 describes an ultrasound diagnostic apparatus whereinan ultrasound probe is comprised of a transducer array and a housing forholding the transducer array, and wherein the transducer array isdetachably mounted to the housing.

CITATION LIST

Patent Literature 1: JP 2003-190159 A

Patent Literature 2: JP 2009-50992 A

SUMMARY OF THE INVENTION

In the ultrasound probe of the apparatus described in Patent Literature1, because the transducer head containing the transducer array isdetachable from the beamforming module, a transducer array having anappropriate frequency band according to the diagnosis purpose can beused. However, such configuration has a problem in which the beamformingmodule is required to have therein mounted a broadband preamplifier witha bandwidth of, for example, about 2 to 20 MHz in order to enableoperation with a plurality of transducer arrays having differentfrequency bands, and a pulser capable of a high drive voltage for atransducer array having a maximum drive voltage among the plurality oftransducer arrays, resulting in increased dimensions of the apparatus.

Likewise, although the ultrasound probe of the apparatus described inPatent Literature 2 permits use of a transducer array having anappropriate frequency band according to the diagnosis purpose, thehousing is required to have mounted therein a broadband amplifier and ahigh drive-voltage pulser, resulting in increased dimensions of theapparatus.

The present invention has been made to solve the above problems in theart and has an object of providing an ultrasound diagnostic apparatuspermitting interchange of transducer arrays to select one having asuitable frequency band for an intended diagnosis purpose, whileachieving reduction in dimensions and improvement of operability.

An ultrasound diagnostic apparatus according to the present inventioncomprises: an ultrasound probe including a transducer array; and a backunit connected to the ultrasound probe by wireless communication andgenerating an ultrasound image based on reception signals outputted fromthe transducer array, wherein the ultrasound probe includes a middleunit connected to the back unit by wireless communication and a frontunit detachably connected to the middle unit and including thetransducer array, and wherein the front unit has a transmission driverthat supplies drive signals to the transducer array and causes thetransducer array to transmit an ultrasonic beam and a preamplifier thatamplifies reception signals outputted from the transducer array.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an ultrasounddiagnostic apparatus according to Embodiment 1 of the invention.

FIG. 2 is a flow chart illustrating the operation of Embodiment 1.

FIG. 3 is a flow chart illustrating an examination mode in Embodiment 1.

FIG. 4 is a block diagram illustrating a configuration of a front unitused in Embodiment 2.

FIG. 5 is a block diagram illustrating a configuration of a front unitused in Embodiment 3.

FIG. 6 is a block diagram illustrating a configuration of a front unitused in a variation of Embodiment 3.

FIG. 7 is a block diagram illustrating a configuration of a front unitused in Embodiment 4.

FIG. 8 is a block diagram illustrating a configuration of a front unitused in a variation of Embodiment 4.

FIG. 9 is a block diagram illustrating a configuration of a middle unitused in Embodiment 5.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below based onthe attached drawings.

Embodiment 1

FIG. 1 illustrates a configuration of an ultrasound diagnostic apparatusaccording to Embodiment 1 of the invention. The ultrasound diagnosticapparatus comprises an ultrasound probe 1 and a back unit 2 that isconnected to the ultrasound probe 1 via wireless communication.

The ultrasound probe 1 comprises a front unit 3 and a middle unit 4. Thefront unit 3 is detachably connected via a connector 5 to the middleunit 4.

The front unit 3 comprises a one-dimensional or two-dimensionaltransducer array 6 including a plurality of ultrasound transducers. Apreamplifier 8 and a transmission driver 9 are connected in parallel tothe transducer array 6 via a transmission/reception selector switch 7. ACPU (central processing unit) 10 is connected to the transmission driver9.

The middle unit 4 comprises an A/D converter (analog-digital convertercircuit) 11 that is connected to the preamplifier 8 of the front unit 3via the connector 5. A reception signal processor 12 is connected to theA/D converter 11, and a wireless communication unit 14 is connected tothe reception signal processor 12 via a parallel/serial converter 13. ACPU 15 is connected to the reception signal processor 12 and theparallel/serial converter 13, and the CPU 15 is connected to the CPU 10of the front unit 3 via the connector 5.

The transducers of the transducer array 6 each transmit ultrasonic wavesaccording to drive signals supplied from the transmission driver 9 andreceive ultrasonic echoes from a subject to output reception signals.Each of the transducers is constituted, for example, by a vibratorincluding a piezoelectric body made of a piezoelectric ceramic typifiedby PZT (lead zirconate titanate) or a polymeric piezoelectric elementtypified by PVDF (polyvinylidene fluoride) and electrodes provided onboth ends of the piezoelectric body.

When the electrodes of the vibrators are supplied with a pulsed voltageor a continuous-wave voltage, the piezoelectric bodies expand andcontract to cause the vibrators to produce pulsed or continuousultrasonic waves. The ultrasonic waves are combined to form anultrasonic beam. Upon reception of a propagating ultrasonic wave, eachvibrator expands and contracts to produce an electric signal, which isthen outputted as reception signal of the ultrasonic wave.

Under the control of the CPU 10, the transmission/reception selectorswitch 7 selectively connects the transducer array 6 to one of thepreamplifier 8 and the transmission driver 9.

The preamplifier 8 amplifies the reception signals outputted from therespective channels of the ultrasonic transducers of the transducerarray 6.

The transmission driver 9 comprises, for example, a plurality of pulsegenerators and adjusts the delay amounts of drive signals for therespective transducers based on a transmission delay pattern selected bythe CPU 10 so that the ultrasonic waves transmitted from the transducerarray 6 form a broad ultrasonic beam covering an area of a tissue in thesubject and supplies the transducers of the transducer array 6 with theadjusted drive signals.

The CPU 10 controls the transmission driver 9 according to variouscontrol signals transmitted from the CPU 15 of the middle unit 4connected via the connector 5.

The transducer array 6 has a specific frequency band and a specificdrive voltage. The preamplifier 8 used has a frequency bandcorresponding to the frequency band of the transducer array 6. Thetransmission driver 9 used outputs a drive voltage corresponding to thedrive voltage for the transducer array 6.

The A/D converter 11 digitizes the reception signals amplified by thepreamplifier 8.

Under the control of the CPU 15, the reception signal processor 12subjects the reception signals digitized by the A/D converter 11 toquadrature detection or quadrature sampling to produce complex basebandsignals, samples the complex baseband signals to generate sample datacontaining information on the area of the tissue, and supplies thesample data to the parallel/serial converter 13. Otherwise, thereception signal processor 12 may generate sample data by performingdata compression on the data obtained by sampling the complex basebandsignals for high-efficiency coding.

The parallel/serial converter 13 converts the parallel sample datagenerated by the reception signal processor 12 having a plurality ofchannels into serial sample data.

The wireless communication unit 14 performs carrier modulation based onthe serial sample data to generate transmission signals and supplies anantenna with the transmission signals so that the antenna transmitsradio waves thereby to transmit the serial sample data. The modulationmethods that may be employed herein include ASK (Amplitude ShiftKeying), PSK (Phase Shift Keying), QPSK (Quadrature Phase Shift Keying),and 16QAM (16 Quadrature Amplitude Modulation).

The wireless communication unit 14 transmits the sample data to the backunit 2 and receives various control signals from the back unit 2 throughwireless communication with the back unit 2, outputting the receivedcontrol signals to the CPU 15.

Based on the control signal received from the back unit 2, the CPU 15transmits a signal to the CPU 10 of the front unit 3 for the control ofthe transmission driver 9 and controls the wireless communication unit14 so that sample data may be transmitted at a set transmission radiofield intensity.

The connector 5 detachably connects the front unit 3 and the middle unit4 and comprises a reception signal line for transmitting receptionsignals amplified by the preamplifier 8 of the front unit 3 to the A/Dconverter 11 of the middle unit 4 and a communication line fortransmitting signals between the CPU 10 of the front unit 3 and the CPU15 of the middle unit 4.

The ultrasound probe 1 includes a built-in battery, not shown, whichsupplies power to the circuits in the front unit 3 and the middle unit 4in the ultrasound probe 1.

The front unit 3 of the ultrasound probe 1 illustrated in FIG. 1 iscompatible with a sector scan mode.

The back unit 2 includes a wireless communication unit 16. An imageforming unit 18 is connected to the wireless communication unit 16 via aserial/parallel converter 17, and a display unit 19 is connected to theimage forming unit 18. A CPU 20 is connected to the wirelesscommunication unit 16, the serial/parallel converter 17, and the imageforming unit 18. Further, an operating unit 21 for an operator toperform input operations is connected to the CPU 20.

The wireless communication unit 16 transmits various control signals tothe ultrasound probe 1 through wireless communication with theultrasound probe 1. The wireless communication unit 16 demodulates thesignal received by an antenna to output serial sample data.

The serial/parallel converter 17 converts the serial sample dataoutputted from the wireless communication unit 16 into parallel sampledata.

The image forming unit 18 performs reception focusing on the sample datato generate image signals representing an ultrasound diagnostic image.The image forming unit 18 includes a phasing adder and an imageprocessor.

The phasing adder selects one reception delay pattern from a pluralityof previously stored reception delay patterns according to the receptiondirection that is set by the CPU 20 and, based on the selected receptiondelay pattern, provides a plurality of complex baseband signalsrepresented by the sample data with their respective delays and addsthem up to perform the reception focusing. This reception focusingyields a baseband signal (sound ray signal) where the ultrasonic echo iswell focused.

The image processor generates a B-mode image signal, which istomographic image information on, for example, a tissue inside thesubject, according to the sound ray signal generated by the phasingadder. The image processor includes an STC (sensitivity time control)unit and a DSC (digital scan converter). The STC unit corrects the soundray signal for the attenuation due to distance according to the depth ofthe reflection position of the ultrasonic wave. The DSC converts thesound ray signal corrected by the STC unit into an image signalcompatible with an ordinary scanning method of television signals(raster conversion), and generates an image signal through requiredimage processing such as gradation processing.

The display unit 19 displays an ultrasound diagnostic image based onimage signals generated by the image forming unit 18 and includes adisplay device such as LCD.

Based on the instruction inputted by an operator from the operating unit21, the CPU 20 controls the wireless communication unit 16 so thatvarious control signals are transmitted at a set transmission radiofield intensity, causes the image forming unit 18 to generate imagesignals, and causes the display unit 19 to display an ultrasounddiagnostic image.

In Embodiment 1, the front unit 3 of the ultrasound probe 1 isdetachably connected to the middle unit 4 via the connector 5. Thus,with a plurality of front units 3 including transducer arrays 6 havingdifferent frequency bands as well as preamplifiers 8 and transmissiondrivers 9 corresponding to the transducer arrays 6 available for use, afront unit 3 comprising a transducer array 6 having a suitable frequencyband for an intended diagnosis purpose can be selected and connected tothe middle unit 4.

Next, the operation of Embodiment 1 will be described with reference tothe flowchart of FIG. 2.

First, examination information including patient information andexamination instructions is entered from the operating unit 21 of theback unit 2 in the examination information input mode in step S1,whereupon the CPU 20 of the back unit 2 selects one front unit 3containing the transducer array 6 having a suitable or usable frequencyband according to the entered patient information.

In step S2 to follow, the CPU 20 of the back unit 2 inquires of the CPU15 of the middle unit 4 by wireless communication, whereupon the CPU 15of the middle unit 4 checks with the CPU 10 of the front unit 3, so thatthe CPU 20 of the back unit 2 may recognize whether or not the frontunit 3 selected in step S1 has been connected to the middle unit 4.

Upon recognizing that the selected front unit 3 has been connected tothe middle unit 4, the CPU 20 of the back unit 2 awaits the operator'sinstruction to start examination in step S3 and, upon receiving theinstruction to start examination, proceeds to step S4 to execute anexamination mode and, in step S5, awaits the operator's instruction toterminate the examination. When instruction to terminate the examinationis entered, a series of examination processes is terminated, whereaswhen instruction to continue the examination is entered, the CPU 20returns to step S1 to receive examination information again.

In step S4, one or more of previously set examination modes such as Bmode, CF mode, PW mode, and M mode, as shown by way of example in FIG.3, may be selected and executed. The CPU 20 of the back unit 2 checksexamination information entered in step S1 to determine which mode hasbeen designated and, upon verifying designation of B mode in step S11,proceeds to step S12 to execute examination in B mode. Upon verifyingdesignation of CF mode in step S13, the CPU 20 proceeds to step S14 toexecute examination in CF mode. Upon verifying designation of PW mode instep S15, the CPU 20 proceeds to step S16 to execute examination in PWmode. Upon verifying designation of M mode in step S17, the CPU 20proceeds to step S18 to execute examination in M mode. When thetermination of examination carried out based on the current examinationinformation is verified in step S19, the CPU 20 proceeds to step S5shown in FIG. 2.

The examinations in the respective modes are executed as follows.

First, operation control command is transmitted from the CPU 20 of theback unit 2 to the ultrasound probe 1 via the wireless communicationunit 16. The operation control command is received by the wirelesscommunication unit 14 of the middle unit 4 and transmitted to the CPU15. Then, the CPU 15 outputs a command for driving the transducer array6 to the CPU 10 of the front unit 3 via the connector 5.

The CPU 10 of the front unit 3 that received the above command operatesthe transmission/reception selector switch 7 to connect the transmissiondriver 9 to the transducer array 6, and the ultrasound transducersconstituting the transducer array 6 transmit ultrasonic waves accordingto drive signals supplied from the transmission driver 9. Thereafter,the CPU 10 causes the transmission/reception selector switch 7 tooperate so that the preamplifier 8 is now connected to the transducerarray 6, and reception signals outputted respectively from thetransducers of the transducer array 6 that received ultrasound echoesfrom a subject are amplified by the preamplifier 8 and then transmittedto the middle unit 4 via the connector 5.

The reception signals transmitted to the middle unit 4 are digitized bythe A/D converter 11 and supplied to the reception signal processor 12,where sample data is generated. The sample data is serialized throughthe parallel/serial converter 13 and wirelessly transmitted from thewireless communication unit 14 to the back unit 2.

The sample data received by the wireless communication unit 16 of theback unit 2 is converted into parallel data through the serial/parallelconverter 17, whereupon the image forming unit 18 produces an imagesignal appropriate for the executed examination mode, so that thedisplay unit 19 displays an ultrasound diagnostic image based on theimage signal.

As described above, the front unit 3 detachably connected to the middleunit 4 incorporates, besides the transducer array 6 having a specificfrequency band, the preamplifier 8 having a frequency band correspondingto the frequency band of the transducer array 6 and the transmissiondriver 9 for outputting a drive voltage corresponding to the drivevoltage for the transducer array 6. Thus, one need not employ anover-engineered system configuration, as conventionally required,equipped with a broadband preamplifier having a bandwidth of about, forexample, 2 to 20 MHz and enabling operation with a plurality oftransducer arrays having different frequency bands and a transmissiondriver capable of a high drive voltage adapted to a transducer arrayhaving a maximum drive voltage among a plurality of transducer arrays.Thus, a compact ultrasound diagnostic apparatus with enhancedoperability can be realized.

Further, in Embodiment 1 above, the front unit 3 and the middle unit 4are exclusively provided with the CPU 10 and the CPU 15 respectively, sothat the CPU 10 controls the components in the front unit 3 while theCPU 15 controls the components in the middle unit 4. Thus, the number ofcontrol signal lines for connecting the front unit 3 and the middle unit4 can be reduced, and both units can be detachably connected by acompact connector 5.

Embodiment 2

Although the front unit 3 of the ultrasound probe 1 used in Embodiment 1above is compatible with a sector scan mode, the invention is notlimited thereto. The front unit 3 may be compatible with other scanmodes including, for example, a linear scan mode and a convex scan mode.

FIG. 4 illustrates a configuration of a front unit 31 used in Embodiment2. As compared with the front unit 3 in Embodiment 1 illustrated in FIG.1, the front unit 31 has a multiplexer 32 connected between thetransducer array 6 and the transmission/reception selector switch 7 toacquire compatibility with the linear scan mode and the convex scanmode.

Under the control of the CPU 10, some transducers among thoseconstituting the transducer array 6 are sequentially selected andperform transmission and reception of ultrasonic waves. This enablesacquisition of an ultrasound diagnostic image by the linear scan mode orthe convex scan mode.

When equipped with both the front unit 3 compatible with the sector scanmode as illustrated in FIG. 1 and the front unit 31 compatible with thelinear scan mode and the convex scan mode as used in Embodiment 2, onemay select one of these front units according to the scan mode andconnect it to the middle unit 4.

Embodiment 3

FIG. 5 illustrates a configuration of a front unit 41 used in anultrasound diagnostic apparatus according to Embodiment 3. As comparedwith the front unit 3 in Embodiment 1 illustrated in FIG. 1, the frontunit 41 does not have the transmission/reception selector switch 7, andin place of the transducer array 6, has a reception transducer array 42for only reception connected to the preamplifier 8 and a transmissiontransducer array 43 for only transmission connected to the transmissiondriver 9.

The front unit 41 is compatible with the sector scan mode.

Because the reception transducer array 42 dedicated to reception and thetransmission transducer array 43 dedicated to transmission are provided,cross talk occurring in transmission of ultrasonic waves can beprevented and ultrasound diagnosis can be given with enhanced accuracy.

Although the front unit 41 illustrated in FIG. 5 is compatible with thesector scan mode, the invention is not so limited; as in a front unit 51illustrated in FIG. 6, a front unit compatible with the linear scan modeand the convex scan mode may be configured by connecting a multiplexer52 between the reception transducer array 42 and the preamplifier 8 andconnecting a multiplexer 53 between the transmission transducer array 43and the transmission driver 9.

Embodiment 4

FIG. 7 illustrates a configuration of a front unit 61 used in anultrasound diagnostic apparatus according to Embodiment 4. As comparedwith the front unit 3 in Embodiment 1 illustrated in FIG. 1, the frontunit 61 has a harmonic component reception transducer array 62 connectedto the preamplifier 8 in addition to the transducer array 6 used forboth transmission and reception.

The front unit 61 is compatible with the sector scan mode.

The harmonic component reception transducer array 62 is a transducerarray having a frequency band especially adapted to harmonic components.With such a harmonic component reception transducer array 62 provided, aharmonic component can be received by the harmonic component receptiontransducer array 62 while an ultrasonic echo in a basic frequency bandis received by the transducer array 6 that is used for both transmissionand reception, enabling a still more accurate ultrasound diagnosis.

Although the front unit 61 illustrated in FIG. 7 is compatible with thesector scan mode, the invention is not so limited; as in a front unit 71illustrated in FIG. 8, a front unit compatible with the linear scan modeand the convex scan mode may be configured by connecting a multiplexer72 between the transducer array 6 used for both transmission andreception and the transmission/reception selector switch 7 andconnecting a multiplexer 73 between the harmonic component receptiontransducer array 62 and the preamplifier 8.

Embodiment 5

FIG. 9 illustrates a configuration of a middle unit 81 used in anultrasound diagnostic apparatus according to Embodiment 5. As comparedwith the middle unit 4 in Embodiment 1 illustrated in FIG. 1, the middleunit 81 has an operating unit 82 for performing input operation into theultrasound diagnostic apparatus and a display unit 83 for displayinginformation, both of which are connected to the CPU 15.

With the operating unit 82 provided in the middle unit 81 of theultrasound probe 1, various kinds of information may be entered from theultrasound probe 1 connected to the back unit 2 by wirelesscommunication to operate the ultrasound diagnostic apparatus from theultrasound probe 1.

Further with the display unit 83 provided in the middle unit 81 of theultrasound probe 1, such information as a name and a kind of the frontunit connected to the middle unit 81 through the connector 5 can bedisplayed on the ultrasound probe 1, enhancing operability andconvenience.

Although Embodiment 5 includes both the operating unit 82 and thedisplay unit 83 in the middle unit 81, only one of the operating unit 82and the display unit 83 may be connected to the CPU 15 of the middleunit 81.

What is claimed is:
 1. An ultrasound diagnostic apparatus comprising: aplurality of front units including transducer arrays having differentfrequency bands and different drive voltages, transmission driversconfigured to supply drive voltages restricted correspondingly to thetransducer arrays to transmit ultrasonic beams from the transducerarrays, and preamplifiers having frequency bands restrictedcorrespondingly to the frequency bands of the transducer arraysconfigured to amplify reception signals outputted from the transducerarrays; a middle unit connected to a front unit selected according to anintended diagnosis from the plurality of front units and including anA/D converter configured to convert reception signals amplified in theselected front unit into a digital signal, a reception signal processorconfigured to frequency-modulate the digital signal obtained throughconversion by the A/D converter to a baseband frequency, and aparallel/serial, converter configured to serialize the signal that isfrequency-modulated by the reception signal processor, an input deviceperforming input operation into the ultrasound diagnostic apparatus tooperate the ultrasound diagnostic apparatus, and a display unitdisplaying information regarding the selected front unit; a connectordetachably connecting the selected front unit and the middle unit; and aback unit connected to the middle unit by wireless communication andconfigured to generate an ultrasound image based on reception signalsamplified in the selected front unit, wherein by selecting the frontunit according to the intended diagnosis from the plurality of frontunits and connecting the selected front unit to the middle unit throughthe connector, a change to a transducer array having a restrictedfrequency band for the intended diagnosis and a change to a transmissiondriver and a preamplifier corresponding to the transducer array aremade.
 2. The ultrasound diagnostic apparatus according to claim 1,wherein each of the plurality of front units and the middle unit furthercomprise dedicated CPUs and the connector includes a reception signalline for transmitting reception signals amplified in the selected frontunit and a communication line for transmitting signals between both CPUsof the selected front unit and the middle unit.
 3. The ultrasounddiagnostic apparatus according to claim 2, wherein the plurality offront units further comprise multiplexers connected to the transducerarrays.
 4. The ultrasound diagnostic apparatus according to claim 3,wherein each of the transducer arrays of the plurality of front unitscomprises a transmission transducer array dedicated to transmission anda reception transducer array dedicated to reception.
 5. The ultrasounddiagnostic apparatus according to claim 4, wherein the middle unitfurther comprises an A/D converter configured to convert receptionsignals amplified in the selected front unit into a digital signal, areception signal processor configured to frequency-modulate the digitalsignal obtained through conversion by the A/D converter to a basebandfrequency, and a parallel/serial converter configured to serialize thesignal that is frequency-modulated by the reception signal processor. 6.The ultrasound diagnostic apparatus according to claim 3, wherein eachof the transducer arrays of the plurality of front units comprises adual-purpose transducer array for transmission and reception and aharmonic transducer array for harmonic component reception.
 7. Theultrasound diagnostic apparatus according to claim 6, wherein the middleunit further comprises an A/D converter configured to convert receptionsignals amplified in the selected front unit into a digital signal, areception signal processor configured to frequency-modulate the digitalsignal obtained through conversion by the A/D converter to a basebandfrequency, and a parallel/serial converter configured to serialize thesignal that is frequency-modulated by the reception signal processor. 8.The ultrasound diagnostic apparatus according to claim 3, wherein themiddle unit further comprises an A/D converter configured to convertreception signals amplified in the selected front unit into a digitalsignal, a reception signal processor configured to frequency-modulatethe digital signal obtained through conversion by the A/D converter to abaseband frequency, and a parallel/serial converter configured toserialize the signal that is frequency-modulated by the reception signalprocessor.
 9. The ultrasound diagnostic apparatus according to claim 2,wherein each of the transducer arrays of the plurality of front unitscomprises a transmission transducer array dedicated to transmission anda reception transducer array dedicated to reception.
 10. The ultrasounddiagnostic apparatus according to claim 2, wherein each of thetransducer arrays of the plurality of front units comprises adual-purpose transducer array for transmission and reception and aharmonic transducer array for harmonic component reception.
 11. Theultrasound diagnostic apparatus according to claim 2, wherein the middleunit further comprises an A/D converter configured to convert receptionsignals amplified in the selected front unit into a digital signal, areception signal processor configured to frequency-modulate the digitalsignal obtained through conversion by the A/D converter to a basebandfrequency, and a parallel/serial converter configured to serialize thesignal that is frequency-modulated by the reception signal processor.12. The ultrasound diagnostic apparatus according to claim 1, whereineach of the transducer arrays of the plurality of front units comprisesa transmission transducer array dedicated to transmission and areception transducer array dedicated to reception.
 13. The ultrasounddiagnostic apparatus according to claim 1, wherein each of thetransducer arrays of the plurality of front units comprises adual-purpose transducer array for transmission and reception and aharmonic transducer array for harmonic component reception.